\subsection{SOAP \& WSDL}
SOAP (Simple Object Access Protocol) is a protocol invented by the industry. It uses the XML format for messages sent between the client and the server. In terms of RPC (Remote Procedure Call), SOAP is a protocol to specify a remote procedure on a server. On the client side an envelope in XML format is created, which contains a body and optionally a header. The body contains information about which procedure to execute and with which parameters. The server will execute the procedure and return a SOAP envelope in XML format containing the results.

WSDL (Web Services Description Language) is used to specify the format of which an SOAP request/response should look like. The WSDL file specifies which operations are available on a given server. The advantage of WSDL and SOAP is that by using the WSDL specification it is possible for heterogeneous systems to communicate, because they use the common message format. The main disadvantage is the added computations needed for translating request into XML format.
